Adherence to antiretroviral therapy (ART) is a serious challenge for many people living with HIV (PLWH). Inconsistent adherence is associated with poor clinical outcomes, treatment failure, and increased healthcare costs. Pharmacists are uniquely positioned to promote adherence to ART given their proximity to PLWH and training, yet they remain an underutilized resource in the management of HIV infection. Pilot studies indicate that pharmacist-implemented adherence promotion activities (e.g., medication-specific education, follow-ups to monitor adherence), can be highly effective in increasing adherence to ART and improving patient health outcomes. Our preliminary qualitative study indicated that pharmacists in specialty pharmacies already use multiple strategies to prevent and resolve adherence barriers that disrupt therapy, but face challenges that interfere with their ability to promote ART adherence. In particular, we found that some community-based specialty pharmacists routinely provided adherence promotion activities, including adherence assessments using prescription refill history and patient self-reports (e.g., missed doses in the last week), monitoring activities through initial follow up phone calls to new patients and regular phone calls, and individually tailored interventions (e.g., patient education on ARV side effects, patient referrals to other providers), that were above and beyond prescription dispensing services. We found that specialty mail-order pharmacists provided similar adherence promotion activities to community-based specialty pharmacists (e.g., monitoring activities), and that nonspecialty mail-order pharmacies and nonspecialty community-based pharmacies faced similar challenges (e.g., limited patient monitoring). However, because our preliminary study used a small non-random purposive sample and included only 3 mail-order pharmacists, there is a need for a larger quantitative study to assess the generalizability of our findings to other pharmacy settings. The proposed R21 will use a cross-sectional quantitative survey to examine: 1) the extent to which ART adherence promotion activities varies in different pharmacy settings; 2) the direct effects of pharmacist characteristics (knowledge, motivation, behavioral skills); and 3) the potential moderating effects of pharmacy characteristics and insurance policies on the provision of adherence promotion activities. We will recruit 225 pharmacists from 225 pharmacies (75 specialty and 75 nonspecialty pharmacies located in 10 high HIV prevalence MSAs, and 75 mail-order pharmacies from a nationwide sample). Participants will complete either an online or paper survey. We will develop a survey questionnaire drawn from our preliminary qualitative study and relevant published literature. The proposed R21 study is significant in that, to our knowledge, it will be the first to examine how pharmacist factors (knowledge, motivation and behavioral skills), pharmacy environment, and specific insurance policies influence the provision of adherence promotion activities in real world pharmacy settings. Findings from this R21 study can inform the design of: 1) educational, motivational and skill-building interventions to promote pharmacists' involvement in adherence promotion; 2) pharmacy-level interventions (e.g., management support of adherence promotion activities through providing specialized monitoring software, trained pharmacy technicians) to provide environments conducive for adherence promotion practices; and 3) evidence-based policy recommendations including prior authorization exemptions for HIV-related medications to reduce administrative burden and reimbursement for adherence promotion activities to encourage pharmacists to provide these services to PLWH.